Semiconductor Device, Radio Communication Device, and Control Method for Radio Communication Device

1. A semiconductor device, comprising: a receiving unit that receives a radio signal; a received signal strength measurement unit that measures a received signal strength of the received radio signal; a threshold comparison unit that compares the measured received signal strength with a threshold; a demodulation unit that demodulates the received radio signal based on a result of the comparison; and a threshold setting unit that sets the threshold according to the measured received signal strength, wherein the measured received signal strength at is input to the threshold setting unit is a same as the measured received signal strength that is input to the threshold comparison unit.

2. The semiconductor device according to claim 1 , wherein the threshold setting unit sets the threshold based on a distance corresponding to the received signal strength.

3. The semiconductor device according to claim 1 , further comprising a storage unit that stores a threshold table for associating the received signal strength with the threshold, wherein the threshold setting unit refers to the threshold table and sets the threshold corresponding to the received signal strength.

4. The semiconductor device according to claim 1 , wherein, when there is no error in a demodulation result, the threshold setting unit sets the threshold according to the received signal strength.

5. The semiconductor device according to claim 1 , wherein the threshold setting unit sets the threshold based on a result of a comparison between a setting determination threshold and the received signal strength, the setting determination threshold being used for setting the threshold.

6. The semiconductor device according to claim 5 , wherein the threshold setting unit sets a first threshold to the threshold when the received signal strength is smaller than the setting determination threshold and sets a second threshold to the threshold when the received signal strength is larger than the setting determination threshold, the second threshold being larger than the first threshold.

7. The semiconductor device according to claim 1 , wherein the threshold setting unit sets the threshold based on a received signal state corresponding to the received signal strength.

8. The semiconductor device according to claim 7 , wherein, when the received signal strength meets a state transition condition corresponding to the received signal state, the threshold setting unit changes its state to the received signal state and sets the threshold according to the changed received signal state.

9. The semiconductor device according to claim 8 , wherein the state transition condition includes a condition for determining the number of receptions of radio signals having a predetermined received signal strength.

10. The semiconductor device according to claim 8 , wherein, when a first state transition condition is met, the threshold setting unit changes its state from a first received signal state to a second received signal state, and wherein, when a second state transition condition is met, the threshold setting unit changes its state from the second received signal state to the first received signal state, the second state transition condition being different from the first state transition condition.

11. The semiconductor device according to claim 1 , further comprising a reception gain setting unit that sets a reception gain of the receiving unit according to the measured received signal strength.

12. The semiconductor device according to claim 1 , further comprising: a transmitting unit that transmits a radio signal according to transmission data; and a transmission power setting unit that sets transmission power of the transmitting unit according to the measured received signal strength.

13. A radio communication device, comprising: an antenna; a receiving unit that receives a radio signal through the antenna; a received signal strength measurement unit that measures a received signal strength of the received radio signal; a threshold comparison unit that compares the measured received signal strength with a threshold; a demodulation unit that demodulates the received radio signal based on a result of the comparison; and a threshold setting unit that sets the threshold according to the measured received signal strength, wherein the measured received signal strength that is input to the threshold setting unit is a same as the measured received signal strength that is input to the threshold comparison unit.

14. A method for controlling a radio communication device including an antenna, the method comprising: receiving a radio signal through the antenna; measuring a received signal strength of the received radio signal; comparing the measured received signal strength with a threshold; demodulating the received radio signal based on a result of the comparison; and setting the threshold according to the measured received signal strength, wherein the measured received signal strength that is used in the setting the threshold is a same as the measured receive signal strength that is used in the comparing the measured received signal strength with the threshold.

15. The semiconductor device according to claim 1 , wherein the received signal strength measurement unit sends the same measured received signal strength to the threshold setting unit and to the threshold comparison unit.

16. The semiconductor device according to claim 1 , wherein the received signal strength measurement unit directly sends the same measured received signal strength to the threshold setting unit and to the threshold comparison unit.

17. The semiconductor device according to claim 1 , wherein, when there is no error in a demodulation result, the threshold setting unit sets the threshold according to the measured received signal strength, and wherein, when there is the error in the demodulation result, the threshold setting unit maintains a current threshold.

18. The radio communication device according to claim 13 , wherein the received signal strength measurement unit sends the same measured received signal strength to the threshold setting unit and to the threshold comparison unit.

19. The radio communication device according to claim 13 , wherein the received signal strength measurement unit directly sends the same measured received signal strength to the threshold setting unit and to the threshold comparison unit.

20. The radio communication device according to claim 13 , wherein, when there is no error in a demodulation result, the threshold setting unit sets the threshold according to the measured received signal strength, and wherein, when there is the error in the demodulation result, the threshold setting unit maintains a current threshold.